How to reduce update time?

It takes about 2hr 15 mins to run this Stored Procedure below and complete. I need some assistance to how I can improve this update to be shortened? I understand that JOINS can be written as OUTER AND INNER JOIN OR LEFT JOIN. Can anyone help to clarify?

Will indexing be useful if the Product Stock file keeps changing? I receive a new product file in ASCII txt format daily and I generally will truncate the Product Stock table before inserting the new full data.

Introduced in Microsoft SQL Server 2005, the Copy Database Wizard (http://msdn.microsoft.com/en-us/library/ms188664.aspx) is useful in copying databases and associated objects between SQL instances; therefore, it is a good migration and upgrade tool…

Let's review the features of new SQL Server 2012 (Denali CTP3). It listed as below:
PERCENT_RANK():
PERCENT_RANK() function will returns the percentage value of rank of the values among its group.
PERCENT_RANK() function value always in be…